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[209.85.220.65]) by mx.google.com with SMTPS id g15sor45856747qkk.161.2019.08.03.08.53.51 for (Google Transport Security); Sat, 03 Aug 2019 08:53:51 -0700 (PDT) Received-SPF: pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=E4xysODT; spf=pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=htejun@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=wr1/jf7OC4N1CyD2pZrJRAsqKQhTrW81tkA/dMeoZYU=; b=E4xysODT5QEs0YiJh/6lyT4EBx4B7Mz7IMg6xczGcQ0G9Qk2AtE4TXZ+GCBgFJDEi1 lLnFymeOoSvdAYvHJIdCSSrgbeDE4a17sW8u6K0mHvhTIQr7wv8IU/Sst4zTTu0Ui9p9 jfnV5m2JmluBR+fiHIHyCypa6MemIx71M5jmKx6vtYPIEIc/gtcjHdvjaf5qkicR216B vr2TNHeSv9J9+fUNK7YQ/gOyrhWAGf5rfXuyH6O/uIOIbbVZkbs1h8vugk98ksEkGk+E kSQOd/o+FqbgLWKvjIyIdPT1Sa9ivX+Vce/lqYQCUaRKFWaUnKiHZKnPlvGognn7X6L+ Xw7Q== X-Google-Smtp-Source: APXvYqxgFYSi0U8M7Pxq58YMG2KJi0fk/qfGLpdfgkpRW+ewtu0h1e0nP4F1pryg35uOv1I+y7chQA== X-Received: by 2002:a37:6085:: with SMTP id u127mr96259447qkb.25.1564847631510; Sat, 03 Aug 2019 08:53:51 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::7cfa]) by smtp.gmail.com with ESMTPSA id r205sm38568262qke.115.2019.08.03.08.53.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 03 Aug 2019 08:53:50 -0700 (PDT) Date: Sat, 3 Aug 2019 08:53:49 -0700 From: Tejun Heo To: Matthew Wilcox Cc: axboe@kernel.dk, jack@suse.cz, hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, guro@fb.com, akpm@linux-foundation.org Subject: Re: [PATCH 2/4] bdi: Add bdi->id Message-ID: <20190803155349.GD136335@devbig004.ftw2.facebook.com> References: <20190803140155.181190-1-tj@kernel.org> <20190803140155.181190-3-tj@kernel.org> <20190803153908.GA932@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190803153908.GA932@bombadil.infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hey, Matthew. On Sat, Aug 03, 2019 at 08:39:08AM -0700, Matthew Wilcox wrote: > On Sat, Aug 03, 2019 at 07:01:53AM -0700, Tejun Heo wrote: > > There currently is no way to universally identify and lookup a bdi > > without holding a reference and pointer to it. This patch adds an > > non-recycling bdi->id and implements bdi_get_by_id() which looks up > > bdis by their ids. This will be used by memcg foreign inode flushing. > > > > I left bdi_list alone for simplicity and because while rb_tree does > > support rcu assignment it doesn't seem to guarantee lossless walk when > > walk is racing aginst tree rebalance operations. > > This would seem like the perfect use for an allocating xarray. That > does guarantee lossless walk under the RCU lock. You could get rid of the > bdi_list too. It definitely came to mind but there's a bunch of downsides to recycling IDs or using radix tree for non-compacting allocations. Thanks. -- tejun